Array-based endoscopic ultrasound systems operating at frequencies in the 1-10 MHz range are used frequently for laparoscopic imaging where they provide fast scanning rates, dynamic focusing and beam steering. For endoscopic imaging applications requiring higher resolution such as intravascular, intracardiac, transurethral, trans-nasal and transtympanic imaging, ultrasound arrays have been challenging to manufacture owing the small element size, small element pitch and need to package the finished endoscope into a small enough package to enter the required lumens. These applications have, therefore, been served mainly by single element ultrasound endoscopes which, compared to arrays, suffer slower frame rates, a tradeoff between depth of field and lateral resolution and the necessity of having moving parts in the endoscope head which adds bulk and causes unwanted vibrations.
In recent years there has been significant progress in developing fully sampled forward looking high frequency linear array transducers. For most applications a phase-array endoscope would offer significant improvements over a single-element endoscope. However, although the elements are conventionally proportioned in these arrays, the overall packaging of the transducers remains relatively large. This limits the application of the arrays to topical use where images are generated from outside the body.